Marine food web
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- In Antarctica, light is the most important environmental factor
affecting marine organisms. Without it, plants that are the base
of all food chains cannot grow.
- The most important plants in the Southern Ocean are tiny algae
called phytoplankton.
- The main types of algae are diatoms and dinoflagellates.
- Further south, the ice algae that grow under and within pack
ice and snow are also important.
- Algae grow well in Antarctic waters because of a plentiful supply
of nutrients brought to the surface by upwelling warmer water.
- Krill, small animals that feed on phytoplankton, dominate the
zooplankton.
- There are about 600 000 billion krill in the Southern Ocean,
weighing 500 million tonnes. They are the most abundant animal
in the world.
- It is estimated seabirds eat more than 115 million tonnes of
krill per year.
- The Antarctic food web is very sensitive to change. Any change
in the numbers of one species is likely to have major impacts
on others.
- Crabeater seals outnumber all other seals in the world
put together.
Human impacts
- Humans currently harvest about 100 000 tonnes of krill per year,
mostly in the same convenient locations used by seals and penguins.
Dried krill are close to 50% protein and rich in vitamins, so
this harvest can be expected to increase.
- Humans catch large numbers of Patagonian and Antarctic
toothfish, and there is a danger this fishery could be over-exploited.
(Only 120 of the 20 000 known species of fish live south of the
Antarctic Convergence.)
- Long-line fishing kills more than 100 000 seabirds a year.